LTST-S326KGJSKT Dual Color SMD LED Datasheet - Side Looking - Green/Yellow - 20mA - English Technical Document

1. Product Overview

This document details the technical specifications for a dual-color, side-looking Surface Mount Device (SMD) LED. The component integrates two distinct AlInGaP semiconductor chips within a single package, enabling the emission of green and yellow light. Designed for automated assembly processes, it features a water-clear lens and is supplied on tape and reel for high-volume production. The primary application is as an indicator or status light in electronic equipment where space is constrained and a side-emitting profile is required.

2. Technical Parameter Deep Dive

2.1 Absolute Maximum Ratings

The device must not be operated beyond these limits to prevent permanent damage. Key ratings include a maximum DC forward current of 30 mA per chip, a peak forward current of 80 mA (under pulsed conditions with a 1/10 duty cycle), and a maximum reverse voltage of 5 V. The total power dissipation for each chip is limited to 72 mW. The operational ambient temperature range is specified from -30°C to +85°C.

2.2 Electrical & Optical Characteristics

Measured at a standard test current of 20 mA and an ambient temperature of 25°C, the key performance parameters are defined. For the green chip, the typical luminous intensity is 35.0 mcd (millicandelas) with a minimum of 18.0 mcd. The yellow chip is typically brighter at 75.0 mcd, with a minimum of 28.0 mcd. Both chips exhibit a very wide viewing angle (2θ1/2) of 130 degrees, providing broad visibility. The typical forward voltage (VF) for both colors is 2.0 V, with a maximum of 2.4 V. The dominant wavelengths are approximately 571 nm for green and 589 nm for yellow, defining their perceived color.

3. Binning System Explanation

The LEDs are classified into bins based on luminous intensity and dominant wavelength to ensure color and brightness consistency in production.

3.1 Luminous Intensity Binning

The green LED is available in intensity bins M, N, P, and Q, covering a range from 18.0 mcd to 112.0 mcd. The yellow LED uses bins N, P, Q, and R, covering 28.0 mcd to 180.0 mcd. A tolerance of ±15% is applied within each bin.

3.2 Dominant Wavelength Binning

For the green LED only, dominant wavelength bins C, D, and E are defined, corresponding to wavelength ranges of 567.5-570.5 nm, 570.5-573.5 nm, and 573.5-576.5 nm, respectively, with a ±1 nm tolerance per bin. This precise control allows for matching specific color points in an application.

4. Performance Curve Analysis

While specific graphical curves are referenced in the datasheet (e.g., typical characteristics curves on page 6), they generally illustrate the relationship between forward current (IF) and luminous intensity (IV), forward voltage (VF), and the effect of ambient temperature on light output. These curves are crucial for designers to understand the LED's behavior under non-standard operating conditions, such as driving at a current other than 20 mA or in elevated temperature environments.

5. Mechanical & Package Information

5.1 Package Dimensions and Pinout

The LED conforms to an industry-standard SMD package outline. The pin assignment is critical for correct operation: Cathode 2 (C2) is connected to the green chip's anode (common anode configuration is implied), and Cathode 1 (C1) is connected to the yellow chip's anode. The side-looking design means the primary light emission is perpendicular to the mounting plane.

5.2 Recommended Solder Pad Layout

A suggested solder pad footprint is provided to ensure reliable soldering and proper mechanical alignment during the reflow process. Adhering to these dimensions helps prevent tombstoning and ensures good solder joint formation.

6. Soldering & Assembly Guide

6.1 Reflow Soldering Profile

A detailed infrared (IR) reflow profile is recommended for lead-free (Pb-free) solder processes. Key parameters include a preheat stage, a controlled temperature ramp-up, a peak body temperature not exceeding 260°C for 10 seconds, and a controlled cooling phase. This profile is essential to prevent thermal shock and damage to the LED package and internal wire bonds.

6.2 Storage and Handling

The LEDs are moisture-sensitive. If the original sealed moisture-proof bag is opened, the components should be used within one week or stored in a dry environment (≤30°C/60% RH). For storage beyond one week, baking at approximately 60°C for 20 hours is required before soldering to remove absorbed moisture and prevent "popcorning" during reflow.

6.3 Cleaning

If cleaning after soldering is necessary, only alcohol-based solvents like isopropyl alcohol or ethyl alcohol should be used. The LED should be immersed at normal temperature for less than one minute. Other unspecified chemicals may damage the epoxy lens or package.

7. Packaging & Ordering Information

The device is supplied in standard 8mm carrier tape on 7-inch (178mm) diameter reels. Each reel contains 3000 pieces. The tape and reel specifications comply with ANSI/EIA 481 standards, ensuring compatibility with automated pick-and-place equipment. The part number LTST-S326KGJSKT uniquely identifies this dual-color, side-looking variant with water-clear lens.

8. Application Suggestions

8.1 Typical Application Scenarios

This LED is ideal for space-constrained applications requiring status indication from the side of a PCB, such as in slim consumer electronics (phones, tablets), panel-mounted indicators, automotive dashboard lighting, and industrial control interfaces. The dual-color capability allows for displaying two different states (e.g., power on/green, standby/yellow) from a single component location.

8.2 Design Considerations

Designers must include appropriate current-limiting resistors in series with each LED chip. The resistor value is calculated using Ohm's Law: R = (Vcc - VF) / IF, where VF is the forward voltage (use max. 2.4V for design margin) and IF is the desired drive current (≤30 mA DC). Electrostatic Discharge (ESD) precautions are mandatory during handling; workstations and personnel must be properly grounded.

9. Technical Comparison & Differentiation

The key differentiators of this component are its dual-color capability in a side-looking package and the use of AlInGaP technology. AlInGaP LEDs generally offer higher efficiency and better temperature stability for red, orange, and yellow colors compared to older technologies. The side-emitting form factor provides a distinct advantage over top-emitting LEDs when the viewing direction is parallel to the PCB surface.

10. Frequently Asked Questions (FAQs)

10.1 Can I drive both LED colors simultaneously?

Yes, but the total power dissipation and thermal limits must be observed. Driving both chips at their maximum DC current of 30 mA simultaneously would approach the combined power limit, so thermal management or derating may be necessary in high ambient temperatures.

10.2 What is the difference between peak wavelength and dominant wavelength?

Peak wavelength (λP) is the wavelength at the highest point in the LED's spectral output curve. Dominant wavelength (λd) is derived from the color coordinates on the CIE chromaticity diagram and represents the single wavelength of a pure monochromatic light that would be perceived as the same color by the human eye. Dominant wavelength is more relevant for color specification.

10.3 How do I interpret the bin codes when ordering?

For consistent appearance in your product, specify the required luminous intensity bin (e.g., P) and, for green, the dominant wavelength bin (e.g., D). This ensures all LEDs in your production run have closely matched brightness and color.

11. Practical Design Case Study

Consider a portable medical device with a low-profile enclosure. A status LED must be visible through a small side window. Using this dual-color side-looking LED saves PCB area. The green light indicates normal operation (20 mA drive), and the yellow light indicates a low-battery warning (driven at a lower current, e.g., 15 mA, to differentiate brightness). The design uses separate microcontroller GPIO pins and series resistors to control each color independently. The wide 130-degree viewing angle ensures visibility even if the user's viewing angle is not perfectly aligned.

12. Technology Principle Introduction

This LED utilizes Aluminum Indium Gallium Phosphide (AlInGaP) semiconductor material for light emission. When a forward voltage is applied across the p-n junction, electrons and holes recombine, releasing energy in the form of photons. The specific bandgap energy of the AlInGaP alloy determines the wavelength (color) of the emitted light—in this case, green and yellow. The side-looking effect is achieved by mounting the LED chip on its side within the package, with the light-emitting surface facing the side wall of the encapsulating epoxy lens.

13. Technology Trends

The trend in indicator LEDs continues toward higher efficiency (more light output per unit of electrical power), improved color consistency through tighter binning, and increased integration (such as multi-color and addressable LEDs in tiny packages). There is also a focus on enhancing reliability under higher temperature conditions, such as those found in automotive under-the-hood applications or near high-power processors. The drive for miniaturization persists, pushing package sizes smaller while maintaining or improving optical performance.